1. Field of the Invention
The invention relates to a tire pressure indicator, more particularly to one including pressure gauges that have a self-generating power capability.
2. Description of the Related Art
In U.S. Pat. No. 5,289,161, there is disclosed a known tire pressure indicator that includes a set of pressure gauges, each of which is mounted on a corresponding pneumatic tire of a vehicle, and a receiver device. Each pressure gauge wirelessly transmits a pressure signal to be received by the receiver device when the pressure in the corresponding pneumatic tire is not within a predetermined normal operating pressure range. As such, the receiver device can alert the driver of the vehicle in the event of an abnormal tire pressure condition.
Since the receiver device of the known tire pressure indicator is built into an instrument panel of the vehicle or as a separate device to be installed in the driver room of the vehicle, the power source of the vehicle can be used as the power source for the receiver device. However, since the pressure gauges of the known tire pressure indicator are mounted on the tires of the vehicle, battery cells are used as the power source for the pressure gauges. The need to replace the battery cells when they run out of power inconveniences the owner of the vehicle.
In co-pending U.S. patent application Ser. No. 08/898,435, filed on Jul. 22, 1997, the Applicant disclosed a pressure gauge which includes a casing, a signal generating device, and a power supplying device that is disposed in the casing and that is connected electrically to the signal generating device so as to supply the electric power required for operating the latter. The power supplying device includes a self-generating voltage unit, a rechargeable cell unit and a rectifying-and-charging unit. The self-generating voltage unit has a piezoelectric unit and an impact unit that is capable of continuously striking against the piezoelectric unit when the pneumatic tire to which the casing is mounted is in motion so as to enable the piezoelectric unit to generate a voltage output. The rectifying-and-charging unit interconnects the self-generating voltage unit and the rechargeable cell unit to permit charging of the rechargeable cell unit using the voltage output from the self-generating voltage unit. As such, the possibility that the pressure gauge will run out of power can be eliminated to ensure proper operation of the pressure gauge without causing any inconvenience to the owner of the vehicle.